<i>FERMI</i>OBSERVATIONS OF THE VERY HARD GAMMA-RAY BLAZAR PG 1553+113
A. A. AbdoNational Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, USAM. AckermannW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAM. AjelloW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAW. B. AtwoodSanta Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USAM. AxelssonDepartment of Astronomy, Stockholm University, SE-106 91 Stockholm, SwedenL. BaldiniIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyJ. BalletLaboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d'Astrophysique, CEA Saclay, 91191 Gif sur Yvette, FranceG. BarbielliniDipartimento di Fisica, Università di Trieste, I-34127 Trieste, ItalyD. BastieriDipartimento di Fisica “G. Galilei,” Università di Padova, I-35131 Padova, ItalyK. BechtolW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAR. BellazziniIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyB. BerenjiW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAE. D. BloomW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAE. BonamenteDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyA. W. BorglandW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAJ. BregeonIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyA. BrezIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyM. BrigidaDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyP. BruelLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France; [email protected], [email protected], [email protected], [email protected]T. H. BurnettDepartment of Physics, University of Washington, Seattle, WA 98195-1560, USAG. A. CaliandroDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyR. A. CameronW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. A. CaraveoINAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano, ItalyJ. M. CasandjianLaboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d'Astrophysique, CEA Saclay, 91191 Gif sur Yvette, FranceE. CavazzutiAgenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), ItalyC. CecchiDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyÖ. ÇelikCenter for Research and Exploration in Space Science and Technology (CRESST), NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAE. CharlesW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAA. ChekhtmanGeorge Mason University, Fairfax, VA 22030, USAC. C. CheungNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAJ. ChiangW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAS. CipriniDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyR. ClausW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAJ. Cohen-TanugiLaboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, FranceJ. M. ConradDepartment of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, SwedenS. CutiniAgenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), ItalyC. D. DermerSpace Science Division, Naval Research Laboratory, Washington, DC 20375, USAA. De AngelisDipartimento di Fisica, Università di Udine and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Gruppo Collegato di Udine, I-33100 Udine, ItalyF. de PalmaDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyE. do Couto e SilvaW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. S. DrellW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAR. DuboisW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAD. DumoraCNRS/IN2P3, Centre d'Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan 33175, FranceC. FarnierLaboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, FranceC. FavuzziDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyS. FeganLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France; [email protected], [email protected], [email protected], [email protected]W. B. FockeW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. FortinLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France; [email protected], [email protected], [email protected], [email protected]M. FrailisDipartimento di Fisica, Università di Udine and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Gruppo Collegato di Udine, I-33100 Udine, ItalyY. FukazawaDepartment of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, JapanP. FuscoDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyF. GarganoIstituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, ItalyD. GasparriniAgenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), ItalyN. GehrelsNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAS. GermaniDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyB. GiebelsLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France; [email protected], [email protected], [email protected], [email protected]N. GigliettoDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyF. GiordanoDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyT. GlanzmanW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAG. GodfreyW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAI. A. GrenierLaboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d'Astrophysique, CEA Saclay, 91191 Gif sur Yvette, FranceM.-H. GrondinCNRS/IN2P3, Centre d'Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan 33175, FranceJ. E. GroveSpace Science Division, Naval Research Laboratory, Washington, DC 20375, USAL. GuillemotCNRS/IN2P3, Centre d'Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan 33175, FranceS. GuiriecUniversity of Alabama in Huntsville, Huntsville, AL 35899, USAY. HanabataDepartment of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, JapanA. K. HardingNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAM. HayashidaW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAE. HaysNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAD. HoranLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France; [email protected], [email protected], [email protected], [email protected]R. E. HughesDepartment of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USAG. JóhannessonW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAA. S. JohnsonW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAR. P. JohnsonSanta Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USAW. N. JohnsonSpace Science Division, Naval Research Laboratory, Washington, DC 20375, USAT. KamaeW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAH. KatagiriDepartment of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, JapanJ. KataokaDepartment of Physics, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551, JapanN. KawaiCosmic Radiation Laboratory, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, JapanM. KerrDepartment of Physics, University of Washington, Seattle, WA 98195-1560, USAJ. KnödlsederCentre d'Étude Spatiale des Rayonnements, CNRS/UPS, BP 44346, F-30128 Toulouse Cedex 4, FranceM. KocianW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAM. KussIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyJ. LandéW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAL. LatronicoIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyM. Lemoine‐GoumardCNRS/IN2P3, Centre d'Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan 33175, FranceF. LongoDipartimento di Fisica, Università di Trieste, I-34127 Trieste, ItalyF. LoparcoDipartimento di Fisica, “M. Merlin” dell'Università e del Politecnico di Bari, I-70126 Bari, ItalyB. LottCNRS/IN2P3, Centre d'Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan 33175, FranceM. N. LovelletteSpace Science Division, Naval Research Laboratory, Washington, DC 20375, USAP. LubranoDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyG. M. MadejskiW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAA. MakeevGeorge Mason University, Fairfax, VA 22030, USAM. N. MazziottaIstituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, ItalyW. McConvilleNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAJ. E. McEneryNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAC. MeurerDepartment of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, SwedenP. F. MichelsonW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAW. MitthumsiriW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USATsunefumi MizunoDepartment of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
2009en
ABI
Аннотация
We report the observations of PG 1553+113 during the first ∼200 days of Fermi Gamma-ray Space Telescope science operations, from 2008 August 4 to 2009 February 22 (MJD 54682.7–54884.2). This is the first detailed study of PG 1553+113 in the GeV gamma-ray regime and it allows us to fill a gap of three decades in energy in its spectral energy distribution (SED). We find PG 1553+113 to be a steady source with a hard spectrum that is best fit by a simple power law in the Fermi energy band. We combine the Fermi data with archival radio, optical, X-ray, and very high energy (VHE) gamma-ray data to model its broadband SED and find that a simple, one-zone synchrotron self-Compton model provides a reasonable fit. PG 1553+113 has the softest VHE spectrum of all sources detected in that regime and, out of those with significant detections across the Fermi energy bandpass so far, the hardest spectrum in that energy regime. Thus, it has the largest spectral break of any gamma-ray source studied to date, which could be due to the absorption of the intrinsic gamma-ray spectrum by the extragalactic background light (EBL). Assuming this to be the case, we selected a model with a low level of EBL and used it to absorb the power-law spectrum from PG 1553+113 measured with Fermi (200 MeV–157 GeV) to find the redshift, which gave the best fit to the measured VHE data (90 GeV–1.1 TeV) for this parameterization of the EBL. We show that this redshift can be considered an upper limit on the distance to PG 1553+113.
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